The present invention relates to a production system for pneumatic tires; more particularly, the present invention relates to a production system which substantially eliminates requirement for an intermediate stock of green to realize a significantly improved productivity at the green tires building station and also at the vulcanization station.
The productivity required for manufacturing pneumatic tires, in particular pneumatic radial tires, is affected by the capacity of the building process whereby unvulcanized component member of tires are assembled with each other into green tires. Therefore, various proposals have been made which successfully resulted in considerable reduction of the green tire building cycle time and improved building capacity. In view of the improvement achieved with respect to the green tire building process, particular attention has been focused on measures for improving the vulcanizing capacity and thorough research and development have been conducted aiming at an advanced vulcanization process which is performed at a higher temperature to shorten the vulcanization time while maintaining the quality of the tires, besides the improvement of the vulcanizing unit and the vulcanizing mold themselves. As a result, the vulcanization cycle time per one tire has been remarkably shortened than before.
The above-mentioned measures for improving the productivity have been applied mainly to the production of radial ply tires for passenger-cars (xe2x80x9cPSR tiresxe2x80x9d) and radial ply tires for trucks and buses (xe2x80x9cTBR tiresxe2x80x9d) which are accustomed to mass production, though the resultant technology are also applied to other kinds of tires.
In connection with tires of relatively small and intermediate sizes, such as PSR and TBR tires, there is a significant difference between the building cycle time per one green tire and the vulcanization cycle time per one green tire. Typically, the vulcanization cycle time is at least five times longer than the building cycle time.
Under the circumstances, it has been considered inevitable either to accept long stock time and increased stock amount of the green tires, or to perform changeover of the types of tires to be formed at the building station with a higher frequency so as to reduce the average building cycle time including the time required for the changeover.
A frequent changeover in types of green tires to be formed at the building station, however, is quite disadvantageous in that the productivity is remarkably lowered in the entire factory, so that the changeover at the building station has to be minimized. More particularly, a frequent changeover in types of green tires causes unacceptable increase in the kinds of intermediate materials, thereby giving rise to changeover loss, transfer loss and managing loss of the intermediate materials. The result is that not only the productivity is lowered but also a large factory space is required for the temporary storage of the intermediate materials. Moreover, an increased number of conveyors is required for the intermediate materials and the conveying system becomes thereby complicated, making it difficult to advance the automation of the tire production.
On the other hand, it has been considered appropriate that green tires are subjected to vulcanization by as few vulcanizing molds as possible. This is because a segmented mold is typically required for the production of PSR or TBR tires which is relatively complicated in structure and thus costly as compared to conventional two-piece type molds. As known in the art, a segmented mold generally includes a mold main body comprising a number of tread mold pieces forming the outer contour of the tread portion of the tire, and upper and lower side molds forming the side wall portions of the tire, as well as a container comprising segments which are arranged at the periphery of the tread mold pieces so as to be radially movable with respect to the center axis of the mold, a container ring, and a top plate. The structure of the segmented mold becomes further complicated in the case of PSR tires with an elaborated tread pattern, which makes the mold more expensive and requires a considerable amount of man-hours to exchange the mold main body.
Due to these grounds, it has been considered inevitable that the stock amount of green tires waiting for vulcanization is increased and additional storage facilities and associated devices for intermediate stocks of tire component members and green tires are required in a tire factory, including storage spaces, carriage or conveyors, or even warehouses for temporarily storing tire component members and/or green tires. Moreover, a particular attention has to be paid to avoid defects of green tires which may occur during the storage until vulcanization as the case may be.
It is highly desirable that a pneumatic tire production system is capable of significantly reducing the frequency of changeover at the green tire building station in respect of types of tires to be produced so as to improve the average building cycle time per one tire while maintaining the quality of green tires at a high level, and minimizing the loss time for the vulcanization process in order to improve the average vulcanization cycle time and thereby significantly improve the productivity of tires without essentially requiring intermediate stock of green tires.
It is therefore an object of the present invention to provide a pneumatic tire production system which satisfies these requirements.
According to one aspect of the present invention, there is provided a method for producing pneumatic tires, comprising a green tire building step for assembling unvulcanized members of a radial tire into a green tire, said green tire building step being performed in a building cycle time, and a vulcanization step for carrying out vulcanization of the green tire, said vulcanization step being performed in a vulcanizing cycle time which is longer than said building cycle time, wherein pneumatic tires are produced by at least one production line which comprises a green tire building station including at least one set of building drums, and a vulcanization station including at least one vulcanizing unit equipped with a plurality of vulcanizing molds of a number which satisfies a vulcanizing capacity substantially equivalent to the number of green tires formed at said building station within a predetermined unit time.
In this connection, the unit time may be determined as desired, for examples as 30 minutes or one hour. The number of green tires formed per unit time is not necessarily limited to a natural number, and it is in many cases a decimal. In order to prevent the green tire from becoming intermediate stock, according to the present invention, at least one vulcanizing unit is equipped with a plurality of vulcanizing molds of a number which satisfies the vulcanization capacity substantially equivalent to the number of green tires formed at said building station within a predetermined unit time.
According to one advantageous embodiment, the method of the present invention comprises the steps of: continuously producing pneumatic tires of a first type by synchronously building green tires at said building station and synchronously vulcanizing the green tires for the first type at the vulcanizing station; changing-over production of pneumatic tires from said first type to a second type which requires vulcanizing molds of a different type, by exchanging predetermined components of the tire building drums at said building station and synchronously exchanging predetermined vulcanizing molds at said vulcanizing station; and continuously producing pneumatic tires of a second type by synchronously building the green tires at said building station and synchronously vulcanizing the green tire for the second type at the vulcanizing station.
According to another advantageous embodiment, the method of the present invention comprises the steps of: alternately building green tires of a set of first and second types at said building station, and synchronously performing simultaneous vulcanization of the green tires of the set of first and second types at the vulcanizing station; changing-over production of pneumatic tires from the set of first and second types to a set of first and third types, by exchanging predetermined vulcanizing molds at the vulcanization station, the number of which corresponds to said building cycle time inclusive of a building-suspension time required for changing the vulcanizing molds into ones for the third type; and alternately building, synchronously with the exchange of the vulcanizing molds, green tires of the set of first and third types at the building station, and synchronously performing simultaneous vulcanization of the green tires of the set of first and third types at the vulcanizing station.
The word xe2x80x9csynchronousxe2x80x9d as used herein is to be distinguished from xe2x80x9csimultaneousnessxe2x80x9d; rather, it means xe2x80x9cimmediately after completion of vulcanizationxe2x80x9d when there exists a green tire under vulcanization, or when a green tire unloaded to the mold is still waiting for vulcanization. It is in this respect that a predetermined number of molds, which satisfy the vulcanization capacity substantially equivalent to the number of green tires formed at the building station within a predetermined unit time, as described above, are preferably provided for a vulcanizing unit in a vulcanization station which is paired with the green tire building station.
Preferably, the production line for carrying out method of the present invention comprises exchanger means for exchanging said vulcanization molds, said exchanger means being associated with said vulcanizing unit, and an information processor for receiving information from said green tire building station indicating a changeover of the type of pneumatic tires to be produced, and providing an output information to said exchanger means indicating that the vulcanizing molds of the vulcanizing station are to be partly exchanged, whereby a partial exchange of the vulcanizing molds by the exchanger means is performed synchronously with the changeover of the type of pneumatic tires at the green tire building station.
The vulcanizing molds may be comprised of segmented molds each including a plurality of segmented tread mold pieces for forming an outer contour of a tire tread portion, a plurality of segments arranged on an outer peripheral side of the respective tread mold pieces, for radially moving the respective tread mold pieces, and means for automatically locking and releasing said segments to and from the respective tread mold pieces.
In this instance, each vulcanizing unit may include a container ring connected to the above-mentioned segments of the such that a vertical movement of the container ring causes a radial movement of the segments, an upper and a lower side molds which are engageable with the tread mold pieces, and a top plate for urging the upper side mold into engagement with the tread mold pieces, and wherein the vulcanizing molds at the vulcanizing unit are partially exchanged while the vulcanizing unit is out of operation, by (i) releasing said segments from the respective tread mold pieces and moving the container ring upward so that the segments are moved radially outwards, while the upper side mold in engagement with the tread mold pieces is separated from the top plate, and unloading the tread mold pieces and the upper and lower side molds connected therewith, and (ii) loading a plurality of segmented tread mold pieces and upper and lower side molds forming another segmented mold for a pneumatic tire of a different type, in their preliminarily connected and centered state, and moving the container ring downwards, so that said segments are moved inwards and locked with the segmented tread mold pieces while urging the top plate to the upper side mold.
According to another aspect of the present invention, there is provided a system for producing pneumatic tires including at least one production line which comprises: a green tire building station for assembling unvulcanized members of pneumatic tires into green tires, including at least one set of building drums; and a vulcanizing station for vulcanizing the green tires, including at least one vulcanizing unit equipped with a plurality of vulcanizing molds of a number which satisfies a vulcanizing capacity substantially equivalent to the number of green tires formed at said building station within a predetermined unit time.
According to an advantageous embodiment, the system of the present invention further comprises: mold storage means for storing the vulcanizing molds; a preheating chamber for preheating the vulcanizing molds immediately before they are mounted onto the vulcanizing unit; exchanger means for exchanging the vulcanizing molds by mounting or removing them onto or from the vulcanizing unit; and conveyor means for conveying the vulcanizing molds along a path which extends between the mold storage means and the exchanger means through the preheating chamber.
In this instance, the mold storage means may include a storage space in which the vulcanizing molds are stored in vertical arrays, and said preheating chamber is associated with the storage space.
According to another advantageous embodiment of the system, the above-mentioned at least one vulcanizing unit is movable along a path which extends between a first substation where vulcanized tires are unloaded from the vulcanizing molds and unvulcanized green tires are then loaded onto the vulcanizing molds, and a second substation where the vulcanizing molds after the unvulcanized tires have been loaded is supplied with a high temperature pressurized gas for vulcanization of the green tires.
The vulcanizing unit may be a stationary unit which is associated with loader means for unloading vulcanized tires from the vulcanizing molds and loading unvulcanized green tires onto the vulcanizing molds.
Preferably, the system of the present invention further comprises selector means for selecting the type of green tires, and conveyor means for conveying said selected green tires from the building drum at the green tire building station where two types of green tires are alternately built, to the relevant vulcanizing mold at the vulcanization station.
The vulcanizing molds may be segmented molds each including a plurality of segmented tread mold pieces for forming an outer contour of a tire tread portion, a plurality of segments arranged on an outer peripheral side of the respective tread mold pieces, for radially moving the respective tread mold pieces, and means for automatically locking and releasing said segments to and from the respective tread mold pieces.
In this instance, each vulcanizing unit may comprise a container ring connected to said segments such that a vertical movement of the container ring causes a radial movement of the segments, an upper and a lower side molds which are engageable with the tread mold pieces, and a top plate for urging the upper side mold into engagement with the tread mold pieces.